I'd just presume that the number of people submitting links is a relatively small part of the HN population, people who tend to submit tend to be serial submitt

I'd just presume that the number of people submitting links is a relatively small part of the HN population, people who tend to submit tend to be serial submitters, and the current serial submitters have TC and Mashable at the top of their RSS feeds. If I had to guess, I'd say that HN doesn't drive anywhere near the traffic that a Digg or Reddit front-pager does, so there's not nearly as much incentive to try to game it, but that may just be me being naively optimistic. :)